Video over Internet Protocol (IP) is a network-based one-way transmission of video content. A video source transmits video as a unicast or multicast transmission. For a unicast transmission, the broadcasting source replicates the video for each targeted client (or viewer). For a multicast transmission, however, the broadcasting source sends the same signal over the network as a single video transmission, but the video is sent to a selected group of clients.
Over the last few years, there has been interest in live video broadcasting over IP, which is different from other types of communications on the Internet. For example, one primary difference is that live video broadcasting (or streaming) is a one-way communication scheme instead of a two-way communication scheme.
Normally, client-server network architectures are used for video transmissions such as Internet Protocol television (IPTV) while peer-to-peer (P2P) network architectures are typically used for file-sharing environments where reduced transmission costs are more important than download speed. P2P networks efficiently distribute transmission costs among the nodes by eliminating dedicated server functionality.
As shown in FIG. 1, a conventional P2P network 100 includes a plurality of nodes 1101-110N (N≧2), where each node operates as both a “client” and a “server” to the other clients on the network. More specifically, P2P network 100 features multiple nodes (electronic devices) interconnected to each other over communication paths 120. These nodes operate as either super nodes or leave nodes. A “super node” is generally defined as an electronic device with large resources of CPU power and network bandwidth such as client 1101. These types of nodes shield “leave nodes,” which are electronic devices having very limited resources such as client 1102.
P2P network architectures possess a number of drawbacks. For instance, for conventional P2P networks, data starvation occurs when the ratio of super nodes to leave nodes fall below a minimum level. In a file-sharing environment, large variations in downloading time are commonplace. However, such variations are not suitable when supporting live TV broadcasting where data needs to arrive at its destination within a specific time period or the user will experience a disruption in video playback.
Another drawback of conventional P2P networks involves the unpredictable delay experienced when a node joins or leaves the P2P network. A node usually joins a P2P network by connecting to a small group (one or two) of other nodes at a time. During this joining period, if this small group of other nodes leave the network, the node will have to restart the joining process again from the beginning. If a very large number of clients are leaving the network one after the other, a new client joining the network may experience a long delay. This situation can be common in live TV broadcasting, especially at the end of a popular show. Setting high priority to joining nodes over existing nodes does not completely solve the problem because it creates yet another problem by slowing down the exiting nodes from switching to a new channel.